Development, validation and the application of a congener specific photodegradation model for PBDEs /
The thermodynamic properties of 39 PBDEs have been calculated using Gaussian 03 on the B3LYP/6-31G(d)//B3LYP/6-31G(d) level. The PBDE congeners' enthalpies of formation increase with increasing number of bromines and show a strong dependence on the bromine substitution pattern. The effects of bromine substitution pattern have been quantitatively studied by GAM model based on the output of the theoretical calculations. Based on the GAM model, the enthalpies of formation of the 209 PBDE congeners were calculated. A photodegradation model was developed and validated to predict the products, and their relative concentrations, from the photodegradation of PBDEs. Photodegradation experiments were conducted for octa-BDE technical mixture and its individual components together with BDE-209, 184, 100, 99 and 47. Based on the results of the photodegradation experiments, as well as the model predictions, the photodegradation of PBDEs is a first order reaction and, further, the rate determining step is the stepwise loss of bromine. The predicted reaction time profiles of the photodegradation products correlate well with the experimental results. In addition, the photodegradation results were compared with anaerobic biodegradation. The PBDE products measured in the anaerobic biodegradation were found to be the major products in the photodegradation experiments. The photodegradation experiments and the model predictions were also compared with zero-valent iron reduction of BDE-209, 100 and 47 from a previous study and the same products were found in both photo and Fe? degradation. Good correlation between 15 previously reported photodegradation rate constants of PBDE congeners and their calculated LUMO energies was found. This indicates that, similar to the Fe? reduction, debromination by UV light is caused by electron transfer. Furthermore, the rate constants for the three different degradation processes are controlled by C-Br bond dissociation energy. The model was proved to be predictive for the photodegradation of PBDEs and it should be predictive for anaerobic biodegradation and Fe? reduction of PBDEs.
School:Oregon State University
School Location:USA - Oregon
Source Type:Master's Thesis
Keywords:polybrominated diphenyl ethers photodegradation
Date of Publication: